(pompless)

Our 18 year old cat has been having some problems on and off for years
now and they suddenly have gotten worse.....she turns her head from side
to side like she's having a lot of trouble keeping it in her mouth and
getting it down.

I presume that you realize, at age 18, your cat needs more medical scrunity
that ever before. That's old age for cats. If you see your cat have trouble
eating, it's likely it's because your cat has trouble eating. Did you call
your vet? If not..it's time to call so your vet can do a dental exam on your
cat.